The mechanisms of the thermal rearranagements of alkenylallenes will be elucidated by stereochemical and kinetic techniques designed to detect reactive intermediates. Two major reactions will be studied: the eneallene yield (in chemical formula) eneyne Cope rearrangement and the cyclization-hydrogen shift (ene reaction) leading to alkylidenecyclopentenes. Sigmatropic rearrangements and cycloadditions make up an important component of modern synthetic organic chemistry, which in turn is crucial to the preparation of many therapeutic drugs such as carcinostatic agents, modified antibiotics, and vitamins. The applications of sigmatropic rearrangements and cycloadditions to synthesis can benefit in a practical way from a more complete understanding of mechanisms, because such understanding should increase the accuracy with which the reaction course can be predicted, thereby making more efficient the planning of synthetic strategies.